Motor vehicles are increasingly equipped with various safety devices to meet the rising demand for greater safety. In recent years, mounting of external recognition sensors for detecting objects around as safety devices is making progress. Such external recognition sensors include laser radars and millimeter wave radars. By using these devices, it is made possible to detect objects around, alert the driver and/or execute running control processing according to the situation around, and avoid danger. An exemplary way is to detect a vehicle ahead with a laser radar, alert the driver if a risk of collision is recognized and, if the risk of collision is still impossible to avoid, apply an automatic brake thereby to reduce the damage of possible collision. However, an automobile or the like suddenly emerging from sideways cannot be detected by a sensor alone, and the consequent collision cannot be avoided. In this connection, there is an application that detects, by the use of communication independent of a sensor, a situation that cannot be detected by the sensor, and thereby avoids the possible collision.
Also, Patent Literature 1 describes a method by which the level of reliability regarding whether a given vehicle really exists is set by using a degree of multiplicity of detection of the same object by a sensor and communication, and the available application according to that level of reliability.
Further, Patent Literature 2 describes a method by which threshold values are provided regarding errors in the vehicle's speed and position, a vehicle detected by a sensor and communication is identified, and steering information and the like are added by the use of communication to sensor information and utilized as added.